1. Field of the Invention
This invention relates to a structure of a swingarm for a four-wheeled buggy or the like having a saddle seat.
2. Background Art
Japanese Utility Model Publication No. Hei 6-316 discloses a swingarm for a four-wheeled buggy. Front and rear cross members of the swingarm are formed by conventional casting methods and are welded together via a pair of right and left arm members. The front and rear cross members and the right and left arm members, when welded together, define a hexagonal opening in the body of the swingarm.
Generally, in a four-wheeled buggy, a rear swingarm supports right and left rear wheels via an axle which extends across a rear part of the rear swingarm. Such a design provides the rear swingarm with a large torsional rigidity. However, the torsional rigidity is not uniform along the length and width of the rear swingarm. The torsional rigidity should be largest near the front and rear cross members, and gradually become less toward the center of the rear swingarm.
If the right and left arm members are made of pipe material, as demonstrated in the related art, they are unable to cope with the required variations in torsional rigidity; therefore, the conventional rear swingarm must be constructed with a heavy material, and thus the swingarm cannot avoid having higher rigidity than would normally be necessary. Furthermore, when the arm members are assembled by welding, the design of the conventional rear swingarm requires the length of the welded portions of the arm members to be unnecessarily increased which causes an undesirable increase in manufacturing cost.
Additionally, due to the hexagonal opening of the swingarm of the conventional art, the arm members inevitably need to be reinforced using reinforcing patches along points where welding is to occur. In such a case, the foregoing discussed problems are much more pronounced. Moreover, an increase in the weight of the rear swingarm is observed due to the use of the reinforcing patches. The present invention is intended to provide a rear swingarm for a saddle seat vehicle which can overcome the foregoing problems of the related art and can be easily manufactured.